Crain Engineering

 

FAQ's

Frequently Asked Questions:

Answers:

What are the differences between the Life and Lipo/NimH/NiCAD models of the Glow Plug Driver?
The glow plug driver will automatically shut off when the battery voltage gets too low. This is critically important for Lipo and Life batteries since discharging these types of batteries beyond their limits will damage the battery.

In addition to setting the on/off threshold when you press the 'Set' button, the Glow Plug driver will automatically detect the type of battery you are using when you press the 'Set' button. This automatic 'learning' feature can differentiate between LiPo's, NiCad, and NiMH batteries but the voltage ranges of Lipo's and Life batteries overlap making it impossible to differentiate between LiPo's and LiFe's. So a separate version was created specifically for LiFe batteries so an accurate determination can be made to calculate the low voltage turn off.


Can I drive more than one glow plug with the 'Standard' glow plug driver or do I need to purchase the 'Multi' Glow plug driver?
Yes, you can drive multiple glow plugs with the standard driver provided you can connect them in series. The 'Multi' Glow plug driver was designed specifically to drive multiple glow plugs when a series connection is not possible. For example, a four Cylinder engine where the crankcase creates a common ground for each plug. In a case such as this, it is not possible for all four glow plugs to be connected in series because the Crankcase is common to all plugs and a series connection isn't possible.

Also, keep in mind that with a series connection, if one glow plug burns out all plugs will be disabled because the burned out plug breaks the current flow. To avoid this situation, purchase the 'Multi' Glow Plug Driver. With the Multi, each Glow Plug is driven independently so if a plug burns out the others will still function.

To drive two or more glow plugs just connect them in series. The glow plug driver will automatically adjust the voltage in order to drive a constant current to the glow plug. The figure below shows the wiring diagram for a Twin Engine setup.

App Note - dual Glow plug FAQ.png


I understand the Standard Glow Plug Driver can actually drive more than one Glow Plug. So why or when would I use the 'Multi' Glow Plug Driver?
The 'Multi' Glow plug driver was designed specifically to drive multiple glow plugs when a series connection is not possible. For example, a four Cylinder engine where the crankcase creates a common ground for each plug. In a case such as this, it is not possible for all four glow plugs to be connected in series because the Crankcase is common to all plugs and a series connection isn't possible.
In addition, with a series connection, if one glow plug burns out all plugs will be disabled because the burned out plug breaks the current flow. To avoid this situation, purchase the 'Multi' Glow Plug Driver. With the Multi, each Glow Plug is driven independently so if a plug burns out the others will still function.


How do I determine how long the Glow Battery will drive the glow plug?
To get the best energy effeciency, and thus the most drive time of your Glow Battery, the Glow Driver is a PWM (Pulse Width Modulated) type power source. Calculating the battery run time based on the pulse widths and voltages can be confusing. So the best way to calculate the total time your battery will supply the glow plug is to use a straightforward energy equation.

The equation is: Energy = Power * Time ...or in other words... Watt Seconds = Watts * Seconds

I'll use a three cell 11.1 Volt 1600 maH LiPo as an example. Then I'll explain that this size battery is probably much more than you will need.

First, lets look at the voltage and current if a pure DC battery was used to drive your Glow Plug. For the Glow plug used in my Saito 125, a 1.2V NiCad battery will drive a DC current of 3 amps in the glow plug. So the power is 1.2 Volts x 3 Amps = 3.6 Watts.

Next, calculate the total energy available in the LiPo. A Lipo is considered discharged when the cell voltage drops to 3 Volts. Our Glow plug driver will automatically shutoff when an 11.1 Volt three cell Lipo drops to 9.0 Volts. This protects the battery from damage. Let's assume that the voltage drops linearly as it discharges. (Not technically correct but it's a reasonable approximation) That means the average voltage over the life of the charge will be 10.05 Volts. Let's make it simple and just say 10 Volts. So for our 1600 mah 3 cell LiPo the total energy available for a charge is 10 Volts x 1.6 Amp hour = 16 Watt hours. (1000 milliamps = 1 Amp) Now convert Watt hours to Watt seconds.
So 16 Watt hours * 3600 Seconds/Hour = 57600 Watt seconds.

To determine the time our battery will drive the glow plug you now take the total energy available in the battery by the wattage drawn by the glow plug.
So time = (57600 Watt seconds) / (3.6 Watts) = 16000 seconds.
Converting to minutes we get 16000 seconds / (60 seconds/minute) = 266.67 minutes.
Or converting to hours we get 266.67 minutes / (60 minutes/Hour) = 4.44 Hours.

Considering the glow plug will only be on for a few minutes of each flight the 4.44 hours of power in your battery will last a very long time and for many flights. For comparison purposes, I use a very small single cell 500 maH Lipo as the Glow plug battery in my plane. It's very small and lightweight. It lasts me for a full day of flying. Of course the length of your flights, the throttle set point, and the amount of time spent running at slow speed will effect your time.

Finally, the 'C' rating of the battery should be at least 20. The higher the better. Especially for the 'Multi'. If the 'C' rating is too low then the voltage will drop too much when the Glow Plug is on. This will result in a premature 'Low battery Voltage' shutoff.

Use the example above and plug in your battery characteristics into the equations to determine your run time.


How would I connect a Quad Engine Plane such as a B-17 Scale Bomber?
Use the 'Multi' Glow plug driver. The Multi can drive up to four glow plugs.


What Size Glow Battery do you recommend?
Any battery or combination of cells from 1.2V up to 12 Volts will do the job for the Standard Glow Plug Driver. For the 'Multi' use two or three cell Lipo's or LiFe's.

In general I recommend one or two cell LiPo's and LiFe's for the standard Glow plug driver. The three cell batteries are generally targeted for large power requirements which means they tend to be large maH ratings. A three cell battery will just add unnecessary weight for what we are intending them to do. Save money and save weight by using smaller one or two cell batteries.

If you are going to use Nicad or NiMh for the Standard Model then we recommend using at least two cells. Although the standard Glow Plug Driver will work with a single cell Nicad or NiMh, you'll get better results with 2 or more cells because there is more voltage margin for the Glow Plug driver to work with. In other words, as the battery discharges the voltage will slowly drop. The Glow Plug Driver will automatically adjust for this drop and maintain a constant power level delivered to the glow plug if the battery pack voltage is two cells or more. But with a single cell the Glow Plug needs all the voltage the cell can provide. Thus there is very little the driver can do to compensate for voltage drop as the battery discharges.

For the 'Multi' Glow Plug Driver driving 2, 3, or 4 Glowplugs use a two or three cell Lipo or Life battery with a 'C' rating of 20 or more and at least 350maH capacity.


Is the Glow Plug Driver powered from the glow battery or the receiver battery?
The Receiver Battery. The driver looks like a servo to your receiver and gets the small amount of power to operate from the reciever battery pack. The Glow Plug Battery is used exclusively to power the glow plug.


How do I install it?
The Glow plug driver is so small and lightweight we didn't put mounting holes on it. Just stick a piece of Velcro on the back side and mount it anywhere inside the receiver/Servo compartment. Then connect the wiring to your glow plug and battery to the screw type terminal block, plug in the servo connector to your receiver. Finally, mount the LED indicator light in a location you find most convienient. (I drill a small 1/8" hole in the fuselage and CA the Led in place)


The glow adapter that connects to the Glow plug has just a single wire which is the positive wire. Where and how do I hook up the negative wire?
The negative lead connects to the Engine block. See the pictures below.

App Note - AdapterWiring.jpg


There are times that I want the power to the driver "OFF", and the radio "ON", as for instance while priming or choking. Advancing the throttle to "FULL" will turn off the glo power, of course, but is there another way to disable the Glow Driver?
If you are using a dedicated channel to control the Glow driver rather than a Y-connector on your throttle and you have an unused switch on your transmitter, then you can set up this channel so the switch can act as an enable/disable switch. Mix a switch with the throttle so you can completely turn off the glow driver no matter where the throttle is positioned. Just program the channel so the throttle is mixed 100% and then add an additional mix with the switch.


I am driving two glow plugs. Should I purchase the Standard Glow Driver or the Multi?
In the case of driving two glow plugs, either model of glow plug driver will do the job. The tradeoffs are:

- If you are using the standard glow driver to drive two glow plugs in series: If one of the glow plugs burns out the other glow plug will go off too because the circuit will be opened by the burnt out plug. However, the Multi-Glow driver drives each glow plug independently so the good glow plug will still be operational.

- The standard Glow plug driver can detect an open circuit in the glow plug circuitry and will flash the indicator LED to indicate the open circuit condition. Because the multi can drive from one to four glow plugs, it cant determine if one of the outputs has an open circuit or is simply unused. Therefore the Multi does not indicate open circuits.

If maximum reliability is your goal then the Multi is the best choice since a failure in one glow plug will not affect the other. If you really want the open circuit detection and you aren't concerned with the interdependancy of the glow plugs, then the Single Driver is best.